Poster Session I: Does stimulus image quality affect fixational eye movement characteristics?

Drift has been found to be inversely related to visual acuity (higher diffusion constants for observers with lower visual acuity; Clark et. al, 2022). However, it is not clear if this reflects long-term tuning to ocular characteristics, or a more dynamic adjustment to image quality. To test this, fixational eye movements were measured using an AOSLO and stimuli were presented through the imaging system at 30 Hz. Image quality was altered by simulating aberrations. Five participants completed a tumbling E task under three conditions: no aberration, the participant's natural aberration, and 0.25 D defocus. A 1.2 arcmin gap width E was presented as a 543 nm increment on the 840 nm imaging light for 750 ms. Conditions were randomly interleaved, and feedback was given on each trial. As expected, performance was highest with no aberration, followed by the observer's natural aberration and was worst for defocus. However, drift characteristics (bivariate contour ellipse area, BCEA, and diffusion constant) did not vary, suggesting that on a trial-to-trial basis drift was not tuned to stimulus quality. To test whether drift might be tuned over time, two participants repeated the experiment in ordered blocks of trials. There were differences in BCEA between ordered and randomised trials, but these were not consistent between participants. We will present an analysis of the differences found between individuals in terms of the optical aberrations present in their eye.